摘要：The read/write control logic module receives chip select (CS), read (RD), write (WR), and address (A0, A1) signals to generate int

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Today, I will bring you "51 microcontroller basics"

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思维导图

Mind mapping

8255A是一款经典的通用可编程并行接口芯片，在51单片机系统中广泛应用于扩展I/O端口功能。

The 8255A is a classic general-purpose programmable parallel interface chip widely used in 51 microcontroller systems to expand I/O port functionality.

其内部结构包含四个核心组成部分：数据总线缓冲器作为8位双向三态接口，负责与单片机数据总线的所有数据传输；

Its internal structure consists of four core components: the data bus buffer serves as an 8-bit bidirectional tri-state interface responsible for all data transmission with the microcontroller's data bus;

读写控制逻辑模块接收片选（CS）、读（RD）、写（WR）及地址（A0、A1）信号，产生内部操作控制信号；

The read/write control logic module receives chip select (CS), read (RD), write (WR), and address (A0, A1) signals to generate internal operation control signals;

A组和B组控制电路根据CPU写入的控制字，分别设定端口A、C高四位和端口B、C低四位的工作模式；

Group A and Group B control circuits set the operating modes of Port A, the upper four bits of Port C, and Port B, the lower four bits of Port C, respectively, based on the control word written by the CPU;

三个独立的8位I/O端口（PA、PB、PC）提供24条可编程数字接口线，其中端口C还可按位操作，在选通工作模式下作为状态控制信号使用。

Three independent 8-bit I/O ports (PA, PB, PC) provide 24 programmable digital interface lines, with Port C supporting bit-wise operation and serving as status control signals in strobed operation mode.

该芯片采用40引脚DIP封装，引脚功能分为两大类别：与CPU接口侧包括数据总线D0-D7、低电平有效的片选信号CS、读控制RD和写控制WR、地址选择线A1-A0（用于选择内部四个寄存器），以及高电平有效的复位信号RESET；

The chip adopts a 40-pin DIP package with pin functions divided into two major categories: the CPU interface side includes data bus D0-D7, active-low chip select signal CS, read control RD and write control WR, address selection lines A1-A0 (used to select internal four registers), and active-high reset signal RESET;

与外设连接侧则提供三个8位并行端口PA0-PA7、PB0-PB7和PC0-PC7。

The peripheral connection side provides three 8-bit parallel ports PA0-PA7, PB0-PB7 and PC0-PC7.

所有输入输出引脚均与TTL电平兼容，具有较强的驱动能力。

All input/output pins are TTL compatible and have strong driving capability.

8255A的地址分配由硬件连接方式决定。

The address allocation of the 8255A is determined by the hardware connection method.

片选信号CS通常连接到地址总线高位经译码后的输出，形成芯片的基地址，而地址线A1、A0直接连接到地址总线最低两位，产生内部端口偏移地址。

The chip select signal CS is usually connected to the decoded output of the high-order address bus, forming the base address of the chip, while the address lines A1 and A0 are directly connected to the lowest two bits of the address bus, generating internal port offset addresses.

例如当CS接P2.7译码输出，A1、A0分别接地址线A1、A0时，四个寄存器的地址可能为：端口A（0000H）、端口B（0001H）、端口C（0002H）和控制寄存器（0003H）。

For example, when CS is connected to the decoded output of P2.7, and A1 and A0 are connected to address lines A1 and A0 respectively, the addresses of the four registers might be: Port A (0000H), Port B (0001H), Port C (0002H), and Control Register (0003H).

实际地址取决于具体硬件设计，需要根据电路连接计算确定。

The actual address depends on the specific hardware design and needs to be calculated based on the circuit connections.

在51单片机系统中，通过对控制寄存器写入不同的控制字，可设置8255A的三种工作模式：模式0提供基本的输入输出功能；

In 51 microcontroller systems, by writing different control words to the control register, three working modes of the 8255A can be set: Mode 0 provides basic input/output functionality;

模式1支持选通式I/O操作，利用端口C提供中断和握手信号；

Mode 1 supports strobed I/O operation, using Port C to provide interrupt and handshake signals;

模式2使端口A成为双向总线接口。

Mode 2 makes Port A a bidirectional bus interface.

这种灵活性使8255A成为连接打印机、ADC转换器、键盘显示器等外设的理想接口芯片，大大增强了51单片机的I/O扩展能力。

This flexibility makes the 8255A an ideal interface chip for connecting peripherals such as printers, ADC converters, keyboard displays, etc., greatly enhancing the I/O expansion capability of the 51 microcontroller.

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参考资料：谷歌翻译、百度、B站

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